本帖最后由 wendy 于 2013-7-19 15:27 编辑

版本：oracle 10.2.0.4(64bit).

SQL> set autotrace on;

SQL> select min(income_time) from AGG_QUERY_SESSION_DETAIL;

MIN(INCOME_TIME)

-------------------

2011-01-01 00:00:00

Execution Plan

----------------------------------------------------------

-----------------------------------------------------------------------------------------

| Id  | Operation                  | Name                  | Rows  | Bytes | Cost (%CPU)|

-----------------------------------------------------------------------------------------

|   0 | SELECT STATEMENT           |                       |     1 |     8 |   743K  (2)|

|   1 |  SORT AGGREGATE            |                       |     1 |     8 |            |

|   2 |   INDEX FULL SCAN (MIN/MAX)| IDX_QSD_INCOME_TIME11 |   272M|  2081M|            |

-----------------------------------------------------------------------------------------

Note

-----

- 'PLAN_TABLE' is old version

Statistics

----------------------------------------------------------

0  recursive calls

0  db block gets

4  consistent gets

4  physical reads

0  redo size

528  bytes sent via SQL*Net to client

492  bytes received via SQL*Net from client

2  SQL*Net roundtrips to/from client

0  sorts (memory)

0  sorts (disk)

1  rows processed

SQL> select max(income_time) from AGG_QUERY_SESSION_DETAIL;

MAX(INCOME_TIME)

-------------------

2013-07-18 23:59:40

Execution Plan

----------------------------------------------------------

-----------------------------------------------------------------------------------------

| Id  | Operation                  | Name                  | Rows  | Bytes | Cost (%CPU)|

-----------------------------------------------------------------------------------------

|   0 | SELECT STATEMENT           |                       |     1 |     8 |   743K  (2)|

|   1 |  SORT AGGREGATE            |                       |     1 |     8 |            |

|   2 |   INDEX FULL SCAN (MIN/MAX)| IDX_QSD_INCOME_TIME11 |   272M|  2081M|            |

-----------------------------------------------------------------------------------------

Note

-----

- 'PLAN_TABLE' is old version

Statistics

----------------------------------------------------------

1  recursive calls

0  db block gets

4  consistent gets

3  physical reads

0  redo size

528  bytes sent via SQL*Net to client

492  bytes received via SQL*Net from client

2  SQL*Net roundtrips to/from client

0  sorts (memory)

0  sorts (disk)

1  rows processed

SQL> select max(income_time),min(income_time) from AGG_QUERY_SESSION_DETAIL;

MAX(INCOME_TIME)    MIN(INCOME_TIME)

------------------- -------------------

2013-07-18 23:59:40 2011-01-01 00:00:00

Execution Plan

----------------------------------------------------------

------------------------------------------------------------------------------------

| Id  | Operation          | Name                     | Rows  | Bytes | Cost (%CPU)|

------------------------------------------------------------------------------------

|   0 | SELECT STATEMENT   |                          |     1 |     8 |   743K  (2)|

|   1 |  SORT AGGREGATE    |                          |     1 |     8 |            |

|   2 |   TABLE ACCESS FULL| AGG_QUERY_SESSION_DETAIL |   272M|  2081M|   743K  (2)|

------------------------------------------------------------------------------------

Note

-----

- 'PLAN_TABLE' is old version

Statistics

----------------------------------------------------------

2  recursive calls

3  db block gets

4273288  consistent gets

4273185  physical reads

132  redo size

610  bytes sent via SQL*Net to client

492  bytes received via SQL*Net from client

2  SQL*Net roundtrips to/from client

0  sorts (memory)

0  sorts (disk)

1  rows processed

select min(income_time) from table; 走索引；

select max(income_time) from table; 走索引。

select max(income_time),min(income_time) from table;全表扫描。为什么会这样呢？请赐教！